FIG. 1, shows a conventional code division multiple access (CDMA) base station system which comprises a digital channel signal modulation circuit 110, a modulated signal combination circuit 120, a CDMA bandwidth modulation circuit 130, a radio frequency (RF) converting circuit 140, an output amplifying circuit 150 and a band-pass-filtering circuit 160.
The RF converting circuit 140 includes an up-converter (not shown) and the output amplifying circuit 150 includes a high-power amplifier (not shown). At the digital channel signal modulation circuit 110, a digital CDMA signal is multiplied by an assigned Walsh code to generate a modulated signal. At the modulated signal combination circuit 120, the modulated digital CDMA signal from the digital channel signal modulation circuit 110 is combined with other signals received from other digital channel signal modulation circuits (not shown).
At the CDMA bandwidth modulation circuit 130, the combined signal from the modulation signal combination circuit 120 is modulated by multiplying by a pseudo noise code to generate a CDMA transmit intermediate frequency (TxIF) signal. The up-converter (not shown) of the RF converting circuit 140 converts the frequency of the TxIF signal to radio frequency to generate a transmit radio frequency (TxRF) signal.
The TxRF signal is amplified at the output amplifying circuit 150 and then filtered by using an assigned bandwidth at the band-pass-filtering circuit 160.
On the other hand, call-drop occurs frequently when an ordinary base station having a plurality of frequency assignments (FA's) is adjacently aligned to the smaller base station having single FA or fewer FA than the ordinary base station. Hand-off is provided when a caller moves between the FA of the ordinary base station and the FA of the smaller base station, if both FA's are commonly available within coverage of the ordinary base station and the smaller base station. However, call-drop occurs when the caller moves between the FA of the ordinary base station and the FA of the smaller base station, if the FA of the ordinary base station is not available within the coverage of the smaller base station.
In order to prevent the call-drop, a multiple number of beacon signals are transmitted, with predetermined hand-off parameters to induce the hand-off procedure. Each of the beacon signals is transmitted from the base station into the area which is similar to the traffic FA, the FA for each of the beacon signals being available within the adjacent base station of the smaller base station.
FIG. 2 is a block diagram of a conventional beacon operating apparatus 200 used in the CDMA base station. In FIG. 2, the digital channel signal modulation circuit 110, the modulated signal combination circuit 130 and the CDMA bandwidth modulation circuit 120 are combined into one of a CDMA modulation circuit for the traffic FA (or a traffic FA CDMA modulation circuit) 210 and a CDMA modulation circuit for the beacon FA (or a beacon FA CDMA modulation circuit) 220. The traffic FA CDMA modulation circuit 210 is dedicated to traffic FA and connected to the frequency converting circuit 230. The beacon FA CDMA modulation circuit 220 includes N beacon FA modulation circuits 220-1 to 220-N, N being a positive integer and identical to required number of operated beacon signals.
As shown in FIG. 2, each of the beacon FA modulation circuits 220-1 to 220-N is connected to one of its corresponding one of frequency converting circuits 240-1 to 240-N as shown by one of dashed lines and the traffic FA modulation circuit 210 as shown by a solid line.
The N beacon signals are continuously generated and combined with the traffic signal from the frequency converting circuit 230 at the frequency combining circuit 250 to be applied to the output amplifying circuit 150.
However, in the conventional beacon signal operation as described above, the N number of frequency converting circuits 240-1 to 240-N are included in the beacon operating apparatus 200 and each of the frequency converting circuits 240-1 to 240-N generates its corresponding beacon signal continuously. Since the continuously generated beacon signals increase load at the output end, it is required the N up-converters and the high power amplifier or liner power amplifier to sustain the N beacon signals. Since the continuously generated beacon signals increase forward noise during hand-off procedure after the beacon signal acquisition of a caller's terminal, hand-off success rate is decreased.